This invention relates to a fuel injection system for internal combustion engines.
In a conventional fuel injection system of diesel engines, the shaft of the fuel injection pump is connected through a coupling and an automatic timer to the cam shaft of the engine and the fuel from the fuel tank is supplied under pressure into each injector at a predetermined timing in proportion to the number of revolutions of the engine. In the process of delivery of fuel under pressure by the injection pump, when the fuel under high pressure to be supplied into each injector has reached a pressure more than that required to open the needle valve of each injector, the needle valve is lifted to inject fuel into each cylinder.
The amount of injection of fuel varies depending on the amount of forward movement of the control rack provided in the injection pump. The amount of forward movement of the control rack is controlled by a flywheel connected to the shaft of the injection pump through a linkage. The arrangement is made such that the control rack controls the effective stroke of the piston of a jerk pump of the injection pump in proportion to its forward movement thereby controlling the amount of injection of fuel.
Further, the fuel injection timing can be altered by means of the automatic timer in proportion to the revolving speed of the engine. In brief, the arrangement is made such that the injection timing is advanced as the revolving speed of the engine increases.
In such a conventional fuel injection system, however, because each piston for delivering fuel under pressure is driven by the cam mounted on the shaft of the injection pump, the fuel injection pressure in the low revolution range of the engine will become low and therefore the fuel injection in the low revolution range will become unstable causing deviation in the amount of injection of fuel and improper atomization of fuel injected into each cylinder thereby rendering it difficult to rotate the engine smoothly.
Further, the fuel injection timing can be represented as a function of the revolving speed of the engine; however, at the present time the correction of the injection timing to cope with the exhaust gas emission control and the correction thereof in proportion to the amount of injection of fuel are not made at all. Therefore, it is impossible for the above-mentioned fuel injection system to cope with the exhaust gas emission control, the noise control and the improvement of fuel combustion efficiency all of which are expected to become more and more severe in the future.